Let us suppose that the California GOP decided to nominate Box Turtle Ben Domenech to run for Barbara Boxer's Senate seat this year. Since Box Turtle Ben is only 28 years old, the GOP gets an initiative placed on the ballot lowering the age limit for the US Senate to 28, and the initiative passes.

The Democrats file a lawsuit alleging that the new law violates Article I Section 3 of the Constitution, which says that only people 30 and older can serve in the US Senate. The judge rules that the Democrats are right, and as a result the new law is overturned.

See how that works? It's the judge's job to rule on whether or not a law is consistent with the Constitution. And even though the voters of California voted to lower the Senate's age limit to 28, the Constitution takes precedence over state laws, so any state law that conflicts with the Constitution is invalid, no matter how many people voted for it, and that's how the judge has to rule.